Design and Testing of Ejectors for High Temperature Fuel Cell Hybrid Systems

[+] Author and Article Information
Mario L. Ferrari

Thermochemical Power Group (TPG), Dipartimento di Macchine, Sistemi Energetici e Trasporti, Università di Genova, Italymario.ferrari@unige.it

Davide Bernardi

Thermochemical Power Group (TPG), Dipartimento di Macchine, Sistemi Energetici e Trasporti, Università di Genova, Italydavide.bernardi@unige.it

Aristide F. Massardo

Thermochemical Power Group (TPG), Dipartimento di Macchine, Sistemi Energetici e Trasporti, Università di Genova, Italymassardo@unige.it

J. Fuel Cell Sci. Technol 3(3), 284-291 (Feb 10, 2006) (8 pages) doi:10.1115/1.2211631 History: Received November 29, 2005; Revised February 10, 2006

Our goal in this work is the improvement of the ejector performance inside hybrid systems supporting the theoretical activity with experimental tests. In fact, after a preliminary ejector design, an experimental rig has been developed to test single stage ejectors for hybrid systems at different operative conditions of mass flow rates, pressures, and temperatures. At first, an open circuit has been built to perform tests at atmospheric conditions in the secondary duct. Then, to emulate a SOFC anodic recirculation device, the circuit has been closed, introducing a fuel cell volume in a reduced scale. This configuration is important to test ejectors at pressurized conditions, both in primary and secondary ducts. Finally, the volume has been equipped with an electrical heater and the rig has been thermally insulated to test ejectors with secondary flows at high temperature, necessary to obtain values in similitude conditions with the real ones. This test rig has been used to validate simplified and CFD models necessary to design the ejectors and investigate the internal fluid dynamic phenomena. In fact, the application of CFD validated models has allowed us to improve the performance of ejectors for hybrid systems optimizing the geometry in terms of primary and secondary ducts, mixing chamber length, and diffuser. However, the simplified approach is essential to start the analysis with an effective preliminary geometry.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 11

3-D ejector model

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Figure 15

Half velocity profiles along the mixing duct axis

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Figure 10

Validation of the 2-D model with experimental and 0-D results

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Figure 7

Reynolds similitude results

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Figure 6

Pressure and temperature similitude results

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Figure 5

Plant scheme in LabVIEW™

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Figure 4

The ejector test rig: closed loop configuration with the thermal insulation

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Figure 3

The ejector test rig: open loop configuration

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Figure 1

RRFCS 250kW generator module (7)

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Figure 12

Validation of 3-D model with experimental data and 2-D results

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Figure 16

The short mixing duct (back) and the long one (front)

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Figure 17

Comparison of ejector performance with different mixing ducts

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Figure 9

Simplified model validation: different temperature

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Figure 8

Simplified model validation: different pressure levels

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Figure 18

Recirculated mass flows for different nozzle diameters

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Figure 19

Convergent-divergent nozzle on the left and convergent nozzle on the right

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Figure 20

Distortion of the flow

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Figure 21

Recirculation ratio decrease with heat transfer between flows

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Figure 22

The effect of the nozzle diameter tolerance

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Figure 13

Comparison of LES with k-ε and experimental results

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Figure 14

Pressure profiles along the mixing duct axis




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